This invention relates generally to the extraction of chemical vapors from air and more particularly to an improved method and apparatus for extracting chemical vapors and concentrating them in a liquid medium for analysis.
The invention was developed using explosives vapor as a model compound. Following is a description of the application of the chemical vapor sampler using explosives as a typical example. Utility for sampling other chemicals is further provided in the detailed description of the invention as well as the claims.
Hidden bombs, weapons and other concealed explosive devices can be detected by sensing the explosive vapors emitted from the device. It is generally recognized that there are at least three different applications for such a detection system, namely, the processing of people and items such as baggage or mail, the searching of areas by a portable system intended to locate a hidden store of explosives, and the continuous monitoring of an area to detect when an explosive device enters the area. For example, people and luggage can be processed as they enter transportation terminals or other buildings, including post offices, courthouses and auditoriums. Buildings can be searched for explosives if a bomb threat is received or when there is reason to suspect terrorist or sabotage activity. Airports, post offices, courthouses and other buildings that are common targets for terrorist activity can be monitored continuously to determine if an explosive device is brought into the building.
It is also generally recognized that an explosives vapor detection system which meets the varied requirements of these different applications should have three different components. Such a three component system requires a sampler which extracts sample air and concentrates the explosives vapor it contains, an analyzer which can evaluate the sample for the presence of explosives vapor, and a calibration module which periodically checks the performance of the system.
The present invention is directed to an improved process for extracting air samples and concentrating any chemical vapors the samples contain, for example explosives, and also to an improved apparatus for carrying out the process. The device of the present invention is especially well suited for use in a continuous monitoring application such as the monitoring of a transportation terminal. More specifically, the device is primarily intended to be installed in the ventilating ducts of a building to sample the air that is pulled through the duct work.
It is a particular feature of the invention that extremely low vapor concentrations can be collected so that the presence of chemicals can be detected with confidence and reliability. In this respect, it is noteworthy that the device functions on a batch type operating principle by which the chemical vapor contained in the air that is extracted is scrubbed by a minimal quantity of scrubbing liquid, thereby concentrating the vapor sufficiently that even minute amounts of chemical are detectable.
It is another important feature of the invention that the device has a relatively short operating cycle (typically, about 15 minutes) so that, for example, the entry of an explosive device into the monitored area is detected quickly enough that appropriate action can be taken.
It is still another feature of the invention that the device can operate either semi-automatically or under the control of a human operator.
Other and further features of the invention, including novel features of novelty appurtenant thereto, will be discussed in the course of the following description.